Extension/retraction device

ABSTRACT

An extension/retraction device includes a cylindrical stationary leg section having a base at the upper end thereof, a cylindrical movable leg section in which the stationary leg section is fitted so as to be slidable in the longitudinal direction, an engagement tube having an upper end formed in a stepped shape and installed in the stationary leg section so as to be coaxial with the movable leg section and so as to be pivotable about the cylinder axis of the movable leg section, a pressing spring installed within both the movable leg section and the stationary leg section, a pulling spring held within the pressing spring, a guide tube having an upper end affixed to the base and installed in the engagement tube, an engagement section fitted to the lower end of the engagement tube, and a spacer installed between the lower end of the guide tube and the engagement tube.

CROSS-REFERENCE TO RELATED APPLICATIONS Technical Field

This application continuation application and thus claims benefitpursuant to 35 U.S.C. §120, of U.S. patent application Ser. No.14/194,044, which is a continuation application of International PatentApplication No. PCT/JP2011/069844 filed on Aug. 31, 2011, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to an extension/retraction device to beused for a tripod of a camera or the like, and relates more specificallyto an extension/retraction device configured so that the length can beadjusted steplessly and so that the length can be maintained easily.

2. Background Art

In recent years, the change from journalizing processing in whichjournal entries are recorded in a ledger in detail every day tojournalizing processing in which pieces of data are input by installingaccounting software on personal computers has been made in dailyaccount/tax processing jobs in business enterprises, organizations, andsole proprietors.

In general, a tripod of a camera, a stepladder or the like is configuredso that the length of a leg section can be adjusted freely, andfurniture such as a table or a chair is also configured so that thelength of a leg section can be adjusted. As an element (which will behereinafter referred to as an extension/retraction device) for makingthe length of a leg section variable, a structure for fitting a movableleg section at a lower side in or on a stationary leg section at anupper side so as to be extended and retracted freely in the longitudinaldirection and affixing the position of the movable leg section using athumbscrew or the like is known, for example. Such a structure, however,has a problem that operation of a thumbscrew takes time and thereforeadjustment of the length of a leg section cannot be achieved in a shorttime. Therefore, a simple structure for adjusting the length of a legsection efficiently is required in recent years as solution for theabove problem, and some new devices have been made regarding a simplestructure.

For example, Patent Document 1 discloses a tripod named “Tripod forSurveying Machine,” which is configured so that a movable leg issupported on as to be freely slidable along the longitudinal directionwith respect to a stationary leg which has an upper part supported at atripod head section so as to be freely pivotable and so that the movableleg is affixed and held at a desired relative position with respect tothe stationary leg.

The tripod in Patent Document 1 is provided with, as a device foraffixing and holding the movable leg: an engagement member which runsalong the longitudinal direction of the movable leg; a displacementmember which is installed so as to be freely movable integrally with themovable leg and so as to be displaceable between a first state to befrictionally engaged with an engagement member and a second state to beseparated from the engagement member; and a biasing member for biasingthe displacement member to the first state.

Such a structure has an effect that slide movement of the movable leg isregulated when the displacement member is biased by the biasing memberand frictionally engaged with the engagement member. Moreover, such astructure has an effect that slide movement of the movable leg isallowed when the displacement member is separated from the engagementmember against bias force of the biasing member. Accordingly, it ispossible to simply achieve extension/retraction adjustment of a legsection and easily achieve fine adjustment of the height of a tripod.

Moreover, Patent Document 2 discloses a device named“Extension/Retraction Device,” which is an extension/retractionstructure of a leg section that is to be used for a tripod or the likeand is configured so that the length of the leg section can be adjustedeasily and so that the device can be downsized.

The device disclosed in Patent Document 2 is provided with: a legsection which is a hollow cylinder having a window section at a partthereof and which has an open end; an extension/retraction leg sectionwhich has a tip section fitted in the open end of the leg section andwhich can slide at the inside thereof; a spiral length adjustment memberwhich is located in series with the extension/retraction leg sectionfrom the tip section of the extension/retraction leg section; anextension/retraction member which is held inside the leg section andwhich is provided from the tip section of the extension/retraction legsection and located inside or outside the length adjustment member; andan engagement member for engaging at least the length adjustment memberat the window section provided at the leg section.

With such a structure, when the extension/retraction leg section slidesand is inserted into the leg section, the length adjustment memberslides in conjunction therewith and the extension/retraction member isretracted. In addition, when the engagement member is inserted from thewindow section of the leg section at the time the extension/retractionleg section slides to a desired length, the engagement member penetratesa space of the length adjustment member positioned at the windowsection, so that movement of the length adjustment member, theextension/retraction leg section and the extension/retraction member areinhibited. On the other hand, when the engagement member is removed fromthe space of the length adjustment member, bias force of theextension/retraction member, which has been retracted, automaticallyextends the extension/retraction leg section. Moreover, when a pullingspring formed in a spiral shape is used as the length adjustment member,a number of spaces which can be penetrated by the engagement memberexist steplessly, and it is therefore possible to freely achieve lengthadjustment. Furthermore, it is possible to downsize the entire device,since the extension/retraction member is located inside or outside thelength adjustment member.

CITATION LIST

Patent Document 1: Japanese Published Unexamined Patent Application No.2010-286286

Patent Document 2: Japanese Patent No. 4545778

However, in the tripod of the above conventional technology disclosed inPatent Document 1, the engagement state of the displacement member withthe engagement member depends on frictional force which actstherebetween, and therefore there is a fear that the engagement statemay possibly be released easily when strong force is applied to themovable leg to cause slide movement with respect to the stationary leg.That is, there is a problem that such a tripod cannot support a heavyload safely and has limited uses.

Moreover, in the device disclosed in Patent Document 2, an engagementmember is formed to have a projection which is projected outward on theouter circumferential section of the leg section, and therefore, thereis a fear that the engagement member may possibly be an obstacle bytouching the body or the like of the user, for example, when being inuse. Furthermore, it is necessary to provide, in the length adjustmentmember, a long stroke in the radial direction so that the engagementmember is put into the length adjustment member deeply.

SUMMARY OF INVENTION

Various embodiments of the claimed invention for addressing the aboveissues will be explained individually below. As may be required, thecharacteristic operational effects of the embodiments will also bedescribed. One or more embodiments of the claimed invention has beenmade to cope with such a conventional situation, and the object thereofis to provide an extension/retraction device configured so that fineadjustment of the length of a leg section is facilitated and so that, ina length adjustment member, an engagement section can be reliablyengaged without providing the leg section with a long stroke in theradial direction of the leg section.

As the first embodiments of the claimed invention, one or moreembodiments include: a cylindrical movable leg section; a spiral lengthadjustment member which is installed parallel to a longitudinaldirection of the movable leg section; an engagement section which isformed to be able to be engaged with the length adjustment member; anengagement tube on which the engagement section is affixed so as not tobe movable and which is to be fitted in the movable leg section so as tobe slidable in the longitudinal direction; and an extension/retractionmember, which is installed in parallel with the length adjustment memberin the movable leg section, for biasing the engagement tube in adirection of separating from the movable lea section, wherein theengagement tube is installed so as to be pivotable about the center ofthe cylindrical shape of the movable leg section, the length adjustmentmember has one end affixed to the movable leg section and the other endfitted into the engagement tube so as to be freely slidable in thelongitudinal direction, and the engagement section is installed so as topenetrate a space of the length adjustment member while pivoting or soas to be removed from a space while pivoting in conjunction withrelative pivoting of the movable leg section and the engagement tube.

An extension/retraction device having such a structure has an effectthat the extension/retraction member is retracted and the lengthadjustment member slides in the longitudinal direction of the engagementtube when the engagement tube is pushed into the movable leg section.Moreover, the engagement section is engaged with the length adjustmentmember and the position of the movable leg section in the longitudinaldirection with respect to the engagement tube is affixed by a simpleoperation of pivoting the movable leg section with respect to theengagement tube. Furthermore, the extension/retraction device also hasan effect that the position of the movable leg section in thelongitudinal direction with respect to the stationary leg section is setat a short interval by engaging the engagement section for each intervalof a spiral part of the length adjustment member. In addition, there isno fear that the engagement section interferes with theextension/retraction member in the process of engaging the engagementsection with the length adjustment member. Also, theextension/retraction device has an effect that a variation in the totallength of the extension/retraction member in the process of sliding themovable leg section with respect to the stationary leg section issmaller than a case where the length adjustment member is installed inseries with the extension/retraction member.

Moreover, as the second embodiments of the claimed invention, one ormore embodiments are the extension/retraction device further include: astationary leg section in which at least a part of theextension/retraction member and the engagement tube are held and whichis fitted in the movable leg section so as to be slidable in thelongitudinal direction; and a guide member for guiding the stationaryleg section so as not to be pivotable and so as to be slidable withrespect to the movable leg section, wherein an end of the engagementtube is supported by the stationary leg section so as to be pivotable.

An extension/retraction device having such a structure has an effectthat a part of both of the extension/retraction member and theengagement tube projected from the movable leg section is covered withthe stationary leg section.

As the third embodiments of the claimed invention, in one or moreembodiments, the length adjustment member is not installed in theengagement tube so as to be slidable in the longitudinal direction withan end thereof being affixed to the movable leg section but installed onan outer surface of the movable leg section outside the engagement tubewith both ends thereof being affixed, and a window section is formed onat least a part of aside surface of the movable leg section along thecylinder axis so that the engagement section is projected and can beengaged with the length adjustment member.

An extension/retraction device having such a structure has the effect ofthe first embodiments of the claimed invention, and furthermore,checking of the engagement state of the engagement section with thelength adjustment member is facilitated since the length adjustmentmember is installed outside the movable leg section.

As the fourth embodiments of the claimed invention, one or moreembodiments include: a coupling section installed at one of end sectionsof the movable leg section, in which the engagement tube is not fitted,so as to be freely pivotable about the cylinder axis; and a couplingmember for coupling the coupling section with the engagement tube so asnot to be pivotable and so as to be slidable.

An extension/retraction device having such a structure has the effect ofthe third embodiments of the claimed invention, and further has aneffect that the coupling section and the engagement tube do not pivotindependently of each other in the process of pivoting the movable leg.

As the fifth embodiments of the claimed invention, one or moreembodiments are the extension/retraction device, in which the engagementtube is not provided with the engagement section but provided with arecessed groove in which the length adjustment member is held which isprovided at a side surface along the longitudinal direction, the lengthadjustment member is not installed at the movable leg section butinstalled in the recessed groove so as not to come into contact with aninner surface of the movable leg section, and the movable leg section isnot provided with the window section but provided with the engagementsection which is installed on an inner surface so as to be able to beengaged with the length adjustment member with relative pivoting withrespect to the engagement tube.

An extension/retraction device having such a structure has the effect ofthe third and fourth embodiments of the claimed invention, and furtherhas an effect that a projection section is not generated in installationof the engagement section or the length adjustment member on an outersurface of the movable leg section. Moreover, the extension/retractiondevice has an effect that the length adjustment member can be viewedeasily by detaching the movable leg section from the engagement section.

As the sixth embodiments of the claimed invention, one or moreembodiments are the extension/retraction device according to any one ofthe first to fifth embodiments of the claimed invention, in which alength adjustment member laminated annularly is used instead of thespiral length adjustment member.

An extension/retraction device having such a structure has the effect ofthe first to fifth embodiments of the claimed invention, and further hasan effect that the length adjustment member laminated annularly enablesengagement of the engagement section with a space between annularbodies.

As described above, according to the first embodiments of the claimedinvention, it is possible to adjust the total length to a desiredlength. In the process, it is possible to achieve fine adjustment of thelength easily. Moreover, by pivoting the engagement tube, it is possibleto reliably engage the engagement section with the length adjustmentmember without providing the engagement tube with a long stroke in theradial direction of the engagement tube. Furthermore, force required forextension/retraction does not vary widely, and this improves thehandleability.

According to the second embodiments of the claimed invention, it ispossible to prevent an accident that the hand of a user is pinched in anextension/retraction member, for example, in addition to the effect ofthe invention according to Claim 1, since the extension/retractionmember is not exposed. Moreover, it is also possible to avoid asituation that a user touches the engagement tube and the engagementstate of the engagement section when the length adjustment member isreleased erroneously, for example.

According to the third embodiments of the claimed invention, it ispossible to achieve inspection, repair or the like of the engagementsection or the length adjustment member efficiently, in addition to theeffect according to the first embodiments of the claimed invention.Moreover, it is also possible to decrease the diameter of the movableleg section so as to downsize the entire device.

According to the fourth embodiments of the claimed invention, it ispossible to pivot only the movable leg section independently when acoupling section is coupled with another device or the like and theengagement tube is grounded, for example, in addition to provision ofthe effect of the third embodiments of the claimed invention.Accordingly, it is possible to achieve operation to affix the length ofthe extension/retraction device safely and easily.

According to the fifth embodiments of the claimed invention, effects ofsimple appearance and excellent design are provided, in addition to theeffect of the third or fourth embodiments of the claimed invention.Moreover, it is possible to achieve inspection, repair or the like ofthe length adjustment member efficiently.

According to the sixth embodiments of the claimed invention, a lengthadjustment member laminated annularly is provided with a plurality ofplaces to be engaged with the engagement section as with a spiral lengthadjustment member, and therefore it is possible to achieve fineadjustment of the length of the extension/retraction device, in additionto provision of the effect of the first to fifth embodiments of theclaimed invention.

Other aspects and advantages of the claimed invention will be apparentfrom the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a front view for illustrating the appearance of Example 1of an extension/retraction device according to an embodiment of thepresent invention. FIG. 1(b) is a plan view for illustrating theappearance of Example 1 of an extension/retraction device according toan embodiment of the present invention. FIG. 1(c) is a partiallyenlarged view of a cross section indicated by the arrow A-A in FIG.1(a).

FIG. 2 is a longitudinal sectional view of FIG. 1(a).

FIG. 3(a) is a longitudinal sectional view for illustrating a statewhere FIG. 2 is disassembled. FIG. 3(b) is a longitudinal sectional viewfor illustrating a state where FIG. 2 is disassembled.

FIG. 4(a) is an enlarged view of a cross section indicated by the arrowB₁-B₁ in FIG. 1(a). FIG. 4(b) is an enlarged view of a cross sectionindicated by the arrow B₂-B₂ in FIG. 1(a).

FIGS. 5(a) and 5(b) are views wherein a part of FIG. 4(b) is omitted.

FIG. 6(a) is a front view for illustrating the appearance of Example 2of an extension/retraction device according to an embodiment of thepresent invention. FIG. 6(b) is a view for illustrating a state where acover of a pulling spring in FIG. 6(a) is detached. FIG. 6(c) is a sideview of FIG. 6(b).

FIG. 7(a) is a front view for illustrating the appearance of a movableleg section which composes Example 2 of an extension/retraction deviceaccording to an embodiment of the present invention. FIG. 7(b) is afront view for illustrating the appearance of an engagement tube whichcomposes Example 2 of an extension/retraction device according to anembodiment of the present invention.

FIG. 8(a) is a perspective appearance view of an engagement section.FIG. 8(b) is a plan view of an engagement section. FIG. 8(c) is a sideview of an engagement section. FIG. 8(d) is a front view of anengagement section.

FIGS. 9(a) and 9(b) are perspective views for illustrating a variationexample of an engagement section.

FIGS. 10(a) and 10(b) are views wherein the vicinity of an engagementsection and a stopper assist tool is enlarged partially.

FIG. 11(a) is a longitudinal sectional view for illustrating a statewhere a coupling section, a receiver, a guide tube and an engagementtube are assembled. FIGS. 11(b) and 11(c) views for illustrating a statewhere components in FIG. 11(a) are disassembled.

FIG. 12(a) is a longitudinal sectional view for illustrating a statewhere a coupling section, a receiver, a guide tube and a movable legsection are assembled. FIG. 12(b) is a view wherein the vicinity of areceiver in FIG. 12(a) is enlarged partially. FIG. 12(c) is alongitudinal sectional view for illustrating a state where a movable legsection and an engagement tube are assembled.

FIG. 13(a) is a longitudinal sectional view for illustrating a statewhere an engagement tube and an extension/retraction leg section areassembled. FIG. 13(b) is a view wherein the vicinity of a gripper of anengagement tube in FIG. 13(a) is enlarged.

FIG. 14 is a longitudinal sectional view of an extension/retractiondevice illustrated in FIG. 6(a).

FIGS. 15(a) and 15(b) are enlarged views of a cross section indicated bythe arrow E-E in FIG. 6(b).

FIG. 16(a) is a front view for illustrating the appearance of Example 3of an extension/retraction device according to an embodiment of thepresent invention. FIG. 16(b) is a front view for illustrating theappearance of a movable leg section. FIG. 16(c) is a front view forillustrating the appearance of an engagement tube.

FIGS. 17(a) and 17(b) are enlarged views of a cross section indicated bythe arrow H-H in FIG. 16(a).

DETAILED DESCRIPTION

One or more embodiments of the claimed invention will be explained belowwhile referring to figures. An extension/retraction device according toone or more embodiments of the claimed invention is to be used as a legsection of a tripod of a camera, a stepladder, a ladder, a chair or thelike The following description will explain the detailed structure withreference to FIGS. 1 to 17.

Example 1

An extension/retraction device of the present example will be describedusing FIGS. 1 to 5 (corresponding especially to Claim 1 or 2). FIGS.1(a) and 1(b) are a front view and a plan view for respectivelyillustrating the appearance of an extension/retraction device of thepresent example, and FIG. 1(c) is a partially enlarged view of a crosssection indicated by the arrow A-A in FIG. 1(a).

As illustrated in FIG. 1(a), an extension/retraction device 1 a isprovided with: a cylindrical stationary leg section 3 having an upperend attached to a base 2 on which various machinery or the like is to beinstalled; a cylindrical movable leg section 4 in which the stationaryleg section 3 is fitted so as to be slidable in the longitudinaldirection; and an engagement tube 5 which has an upper end 5 a formed ina stepped shape and which is installed within the stationary leg section3 so as to be coaxial with the movable leg section 4. Moreover, an upperend of the engagement tube 5 is attached to the base 2 in such a mannerthat the engagement tube 5 can pivot about the cylinder axis of themovable leg section 4. That is, an upper end of the engagement tube 5 issupported by the stationary leg section 3 via the base 2 in such amanner that the engagement tube 5 can pivot. In addition, an operatinglever 6 is erected on an outer circumferential surface in the vicinityof the upper end. Furthermore, openings 2 a and 3 a (see FIG. 2) throughwhich the operating lever 6 is to be projected are formed on a sidesurface of the base 2 and on a side surface of the stationary legsection 3 respectively along the circumferential directions so as tocorrespond to the excursion. In such a case, when the operating lever 6is pivoted as illustrated by the arrow C₁ in FIG. 1(b), the engagementtube 5 pivots as indicated by the arrow C₂.

An annular gripper 9 is attached to an upper end of the movable leasection 4, and a plug body 7 is fitted to a lower end of the movable legsection 4. It is to be noted that a plurality of slip stopper groovesare formed in an uneven shape on the outer circumferential surface ofthe gripper 9. Moreover, a guide hole 4 a is formed in a long hole shapeon a side surface of the movable leg section 4 along the longitudinaldirection, and a columnar projection 8 is affixed on a side surface ofthe stationary leg section 3 with an upper part thereof being exposedfrom the guide hole 4 a as illustrated in FIG. 1(c). In such a case,when the movable leg section 4 is moved as indicated by the arrow X. thestationary leg section 3 is inserted into the movable leg section 4while the projection 8 is guided by the guide hole 4 a. That is, whenthe movable leg section 4 is slid with respect to the stationary legsection 3, the guide hole 4 a and the projection 8 function as a guidemember for regulating relative pivoting of the stationary leg section 3and the movable leg section 4.

FIG. 2 is a longitudinal sectional view for explaining theextension/retraction mechanism of the extension/retraction device 1 a,FIGS. 3(a) and 3(b) are longitudinal sectional views for illustrating astate where the extension/retraction device 1 a is disassembled. FIGS.4(a) and 4(b) are enlarged views respectively of a cross sectionindicated by the arrow B₁-B₁ in FIG. 1(a) and a cross section indicatedby the arrow B₂-B₂. FIGS. 5(a) and 5(b) are views for explaining a statewhere the engagement section is engaged with a pulling spring 11 andcorresponds to a view wherein a part of FIG. 4(b) is omitted. It is tobe noted that constituent elements other than the pulling spring 11 anda core 12 are displayed in a cross section in FIG. 2, and hatching whichindicates a cross section regarding a pressing spring 10 is omitted inFIGS. 2 and 3(b). Moreover, in order to clarify the positions of theline B₁-B₁ and the line B₂-B₂ illustrated in FIG. 1(a) in the axialdirection with respect to the engagement tube 5, the lines are alsoillustrated in FIG. 2. In addition, illustration of the pulling spring11 is omitted in FIG. 3(b). Furthermore, like symbols are attached inFIGS. 2 to 4 to constituent elements illustrated in FIG. 1, andexplanation thereof is omitted.

As illustrated in FIGS. 2 to 4, the pressing spring 10 is installedwithin the movable leg section 4 and the stationary lea section 3, andthe pulling spring 11 is held within the pressing spring 10. It is to benoted that “a pressing spring” in the present specification refers to anelement, which is a spiral elastic member having a space under normalcondition and exhibits a reaction force when the total length isretracted with a spiral interval being narrowed, and “a pulling spring”refers to an element, which is a spiral elastic member having littlespace under normal condition and exhibits a reaction force when thetotal length is extended with a spiral interval being widened. Here, thereaction force of such “a pulling spring” is not absolutely necessary,and therefore an extension/retraction device 1 a of the present examplecan use a member in the same shape (a spiral member) having no elasticforce instead of “a pulling spring.”

Installed within the pulling spring 11 is a semicolumnar core 12 havingan upper end 12 a formed in a stepped shape and a lower end 12 b affixedto the plug body 7. In addition, an upper end 10 a of the pressingspring 10 abuts the upper end 5 a of the engagement tube 5, and a lowerend 10 b of the pressing spring 10 is affixed to the plug body 7. Thatis, the pressing spring 10 functions as an extension/retraction memberfor biasing the engagement tube 5 in a direction separating from themovable leg section 4.

Moreover, an upper end 11 a and a lower end 11 b of the pulling spring11 are respectively affixed to the upper end 12 a of the core 12 and tothe plug body 7. On the other hand, installed within the engagement tube5 is a guide tube 13 having an upper end 13 a affixed to the base 2, andthe upper ends 11 a and 12 a of both of the pulling spring 11 and thecore 12 are installed within the guide tube 13 so as to be slidable inthe longitudinal direction. Moreover, an engagement section 14 is fittedto a lower end 5 b of the engagement tube 5.

Moreover, a spacer 15 is installed between a lower end 13 b of the guidetube 13 and the engagement tube 5. It is to be noted that only an innercircumferential surface 15 a of the spacer 15 is affixed to the guidetube 13 (see FIG. 4(a)) so as not to hamper pivoting of the engagementtube 5. In addition, a stopper 14 a having a falcate planar view isattached to an end section of the engagement section 14 as illustratedin FIGS. 3(a) and 4(b).

When the operating lever 6 is operated in the state illustrated in FIG.5(a) so as to pivot the engagement tube 5 in the direction of the arrowD₁, the stopper 14 a pivots together with the engagement tube 5 asillustrated in FIG. 5(b) and is pushed into a spiral space of thepulling spring 11. Thus, movement of the pulling spring 11 is inhibited.Here, the position of the movable leg section 4 in the longitudinaldirection with respect to the stationary leg section 3 is affixed, sincethe lower end 11 b of the pulling spring 11 is connected with themovable leg section 4 via the plug body 7 and the engagement tube 5 isconnected with the stationary leg section 3 via the base 2. At thistime, the pulling spring 11 functions as a length adjustment member.That is, the extension/retraction device 1 a has an effect that thelength is decided by pivoting the engagement tube 5 and engaging theengagement section 14 with the pulling spring 11 which is a lengthadjustment member.

It is to be noted that, when the operating lever 6 is operated from thestate illustrated in FIG. 5(b) so as to pivot the engagement tube 5 inthe direction of the arrow D₂, the engagement section 14 pivots togetherwith the engagement tube 5 as illustrated in FIG. 5(a) and the stopper14 a is removed from a spiral space of the pulling spring 11, andtherefore the engagement state of the engagement section 14 with thepulling spring 11 is released. As a result, it becomes possible toextend and retract the extension/retraction device 1 a.

The extension/retraction device 1 a having such a structure has aneffect that, when the stationary leg section 3 is pushed into themovable leg section, the pressing spring 10 is retracted and the pullingspring 11 slides in the longitudinal direction in the engagement tube 5.Moreover, the extension/retraction device 1 a also has an effect thatthe position of the movable leg section 4 in the longitudinal directionwith respect to the stationary leg section 3 is set at a short intervalby engaging the engagement section 14 for each interval in a spiralsection of the pulling spring 11.

Furthermore, the pulling spring 11 and the engagement section 14 areheld in the pressing spring 10, and therefore there is no fear that theengagement section 14 interferes with the pressing spring 10 in theprocess of engaging the engagement section 14 with the pulling spring11. Moreover, the extension/retraction device 1 a also has an effectthat a variation in the total length of the pressing spring 10 in theprocess of sliding the movable leg section 4 with respect to thestationary leg section 3 is smaller than a case where the pulling spring11 is installed in series with the pressing spring 10.

It is to be noted that it is required, in a structure wherein anengagement blade (corresponding to the stopper 14 a in theextension/retraction device 1 a) in the diameter direction of thepulling spring 11, to set the diameter of the pulling spring 11 large soas to avoid a situation that the contact area of the engagement bladewith a wire of the pulling spring 11 becomes small. On the contrary,with the extension/retraction device 1 a having a structure wherein thestopper 14 a penetrates a spiral space of the pulling spring 11 whilepivoting, it is not necessary to provide a stroke of the stopper 14 a inthe diameter direction of the pulling spring 11, and therefore it ispossible to set the diameter of the engagement tube 5 small. Moreover, asufficient contact area of the stopper 14 a with a wire of the pullingspring 11 can be secured even when the diameter of the pulling spring issmall.

As described above, it is possible with the extension/retraction device1 a to adjust the total length to a desired length, in the process, itis also possible to achieve fine adjustment of the length easily.Moreover, it is also possible to reliably engage the engagement section14 with the pulling spring 11 by a simple operation of operating theoperating lever 6 so as to pivot the engagement tube 5. In such a case,it is not necessary to provide the engagement tube 5 with a long strokein the diameter direction of the engagement tube 5.

Furthermore, force required for extension/retraction of the total lengthdoes not vary widely, and this improves the handleability. Also, thepressing spring 10 and the engagement tube 5 are covered completely withthe stationary leg section 3 and the movable leg section 4, andtherefore it is possible to avoid an accident that a hand of a user ispinched in the pressing spring 10 or an accident that a user touches theengagement tube 5 and the engagement state of the engagement section 24with the pulling spring 11 is released erroneously.

Also, it is possible to decrease the diameter of the engagement tube 5or the pulling spring 11 so as to achieve weight reduction of the entiredevice.

Example 2

Next, an extension/retraction device of the present example will bedescribed using FIGS. 6 to 15 (corresponding especially to Claims 3 and4). FIG. 6(a) is a front view for illustrating the appearance of anextension/retraction device 1 b of the present example, FIG. 6(b) is aview for illustrating a state where a cover 20 of a pulling spring 11 inFIG. 6(a) is taken out, and FIG. 6(c) is a side view of FIG. 6(b).

Moreover, FIGS. 7(a) and 7(b) are front views for illustrating theappearance respectively of a movable leg section 18 and an engagementtube 19. FIGS. 8(a) to 8(d) are respectively a perspective appearanceview, a plan view, a side view and a front view of an engagement section24. FIGS. 9(a) and 9(b) are perspective views for illustrating avariation example of an engagement section 24. FIGS. 10(a) and 10(b) areviews wherein the vicinity of the engagement section 24 and a stopperassist tool 26 in FIG. 7(a) is enlarged partially. It is to be notedthat illustration of the engagement tube 18 is omitted in FIG. 10.

FIG. 11(a) is a longitudinal sectional view for illustrating a statewhere a coupling section 16, a receiver 17, a support body 27 a, a guidetube 27 b and the engagement tube 19 are assembled, and FIGS. 11(b) and11(c) are views for illustrating a state where components in FIG. 11(a)are disassembled. Moreover, FIG. 12(a) is a longitudinal sectional viewfor illustrating a state where the coupling section 16, the receiver 17,the support body 27 a, the guide tube 27 b and the movable leg section18 are assembled, FIG. 12(b) is a view wherein the vicinity of thereceiver 17 in FIG. 12(a) is enlarged partially, and FIG. 12(c) is alongitudinal sectional view for illustrating a state where the movableleg section 18 and the engagement tube 19 are assembled.

Furthermore, FIG. 13(a) is a longitudinal sectional view forillustrating a state where the engagement tube 19 and anextension/retraction leg section 21 are assembled, and FIG. 13(b) is aview wherein the vicinity of an adjustment tool 22 b of the engagementtube 19 in FIG. 13(a) is enlarged. In addition, FIG. 14 is alongitudinal sectional view of the extension/retraction device 1 billustrated in FIG. 6(a), and FIGS. 15(a) and 15(b) are enlarged viewsof a cross section indicated by the arrow E-E in FIG. 6(b). It is to benoted that illustration of the stopper assist tool 26 and a columnarbody 26 b is omitted in FIG. 15. The same symbols are attached toconstituent elements illustrated in FIGS. 1 to 5, and explanationthereof is omitted.

As illustrated in FIGS. 6 and 7 the extension/retraction device 1 b isprovided with: the coupling section 16 to be coupled with another deviceor a member; the receiver 17 on which the coupling section 16 ismounted, a cylindrical movable leg section 18 having an upper end whichis connected with the coupling section 16 via the receiver 17 so as tobe freely pivotable; the engagement tube 19 which is fitted in themovable leg section 18 so as to be freely slidable; the pulling spring11 which is installed on a side surface of the movable leg section 18parallel to the cylinder axis of the movable leg section 18; the cover20 formed over the pulling spring 11; and the extension/retraction legsection 21 to be fitted in the engagement tube 19 so as to be freelyslidable.

Moreover, an annular gripper 22 a and the adjustment tool 22 b areattached to a lower end respectively of the movable lea section 18 andthe engagement tithe 19, and plug bodies 23 a and 23 b are fittedrespectively to upper end of the movable leg section 18 and a lower endof the extension/retraction leg section 21. Furthermore, the engagementsection 24 is affixed on a side surface of the engagement tube 19 in thevicinity of the upper end of the engagement tube 19, and the stopperassist tool 26 is fitted on the pulling spring 11 so as to be freelyslidable in the axial direction. In addition, a window section 18 a isformed on a side surface of the movable leg section 18 along thecylinder axis so that the engagement section 24 is projected and can beengaged with the pulling spring 11.

As illustrated in FIGS. 8(a) to 8(d), the engagement section 24 erectedon a mounting plate 25 has substantially a trapezoidal planar view, andhas a convex section 24 a provided substantially at the center of theengagement section 24 and a blade section 24 c formed in a sharp shape.It is to be noted that an edge of the convex section 24 a is formed inan arc-like shape so as to be able to be engaged with a wire 11 c of thepulling spring 11. Accordingly, when the engagement section 24approaches the pulling spring 11 and the blade section 24 c penetrates aspiral space of the pulling spring 11, the wire 11 c of the pullingspring 11 is engaged with the convex section 24 a (see FIG. 8(c)).Moreover, a coupling section 24 b to be coupled with the engagement tube19 is formed in an arc-like shape having the same curvature as a sidesurface of the engagement tube 19. In addition, a side surface 25 a ofthe mounting plate 25 is coupled with a side surface of the engagementtube 19 together with the coupling section 24 b of the engagementsection 24. Thus, the coupling strength of the engagement section 24with the engagement tube 19 is enhanced.

It is to be noted that the engagement section 24 may be provided withoutthe convex section 24 a but a concave section 24 e having an arc-likeshape with substantially the same radius as the pulling spring 11 asillustrated in FIG. 9(a). With such a structure, when the engagementsection 24 approaches the pulling spring 11 from a state illustrated inFIG. 9(a) and the blade section 24 c penetrates a spiral space of thepulling spring 11 as illustrated in FIG. 9(b), the pulling spring 11 isfitted into the concave section 24 e. Thus, the blade section 24 crarely comes off the pulling spring 11, and the engagement state of theengagement section 24 with respect to the pulling spring 11 is affixed.

Moreover, as illustrated in FIG. 10, the stopper assist tool 26 to befitted on the pulling spring 11 is a cylindrical body having an opening26 a substantially at the center of the stopper assist tool 26 in thelongitudinal direction, and a pair of columnar bodies 26 b and 26 b areerected on aside surface of the stopper assist tool 26 with the opening26 a being sandwiched therebetween. Furthermore, the columnar bodies 26b and 26 b are installed parallel to the cylinder axis of the stopperassist tool 26 and with a predetermined interval so that the mountingplate 25 can be located therebetween. It is to be noted that the pullingspring 11 moves with pivoting of the movable leg section 18 as will bedescribed later. The engagement section 24 is located between thecolumnar bodies 26 b and 26 b together with the stopper assist tool 26so that the blade section 24 c is inserted into and detached from aspace of the pulling spring 11 at this time.

As illustrated in FIGS. 11(a) to 11(c), the receiver 17 has an annularshape, and the coupling section 16 is affixed with a lower sectionthereof being fitted in the receiver 17. Moreover, the rod-shapedsupport body 27 a is erected at the center of the coupling section 16,and the guide tube 27 b having a square tube shape is affixed so as tobe fitted on the support body 27 a. Furthermore, an inner tube 28 islocated within the engagement tube 19 so as to be coaxial with theengagement tube 19, so that a double tube structure is formed.

In addition, an upper end of the inner tube 28 is affixed to theengagement tube 19 via the spacer 29, and a lower end of the inner tube28 is closed by the plug body 30. Moreover, a rod-shaped guide member 31to be fitted in the guide tube 27 b is erected at the center of the plugbody 30, and a spacer 31 a having a square tube shape is attached to anupper section of the guide member 31 so as to be engaged with the guidetube 27 b and inhibit pivoting of the guide member 31 in thecircumferential direction.

In addition, the spacer 31 a is freely slidable in the direction of thecylinder axis within the guide tube 27 b. That is, the guide tube 27 b,the guide member 31 and the spacer 31 a function as a coupling memberfor coupling the coupling section 16 with the engagement tube 19 so asnot to be pivotable and so as to be slidable. Although the spacer 31 ahaving a square tube shape is installed so as to be slidable within theguide tube 27 b having a square tube shape in the present example, it isto be noted that the guide tube 27 b and the spacer 31 a do not need tohave such a shape. For example, the guide tube 27 b may have acylindrical shape, a guide hole may be provided as in Example 1, and aprojection to be guided by the guide hole may be provided at the guidetube 31 instead of the spacer 31 a.

As illustrated in FIGS. 12(a) and 12(b), a plug body 32 provided with athrough hole 32 a, into which the support body 27 a is to be inserted,at the center is fitted to an upper end of the movable leg section 18.In addition, a stepped section 32 b is formed at the plug body 32 so asto project in the radius direction to be engaged with a stepped section17 a of the receiver 17 in a state where the plug body 32 is engagedwith the movable leg section 18. Furthermore, the engagement tube 19 isfitted in the movable leg section 18 so as to be freely slidable asillustrated in FIG. 12(c).

It is to be noted that the plug body 32 is first fitted on the supportbody 27 a so as to be freely pivotable in the circumferential directionin order to attach the movable leg section 18 or the guide tube 27 b tothe coupling section 16 and obtain the state in FIG. 12(a). Next, theguide tube 27 b is fitted on the support body 27 a and affixed so as notto be pivotable and so as not able to be inserted or removed, and thenthe plug body 32 is fitted to the movable leg section 18 so as not to bedetached.

Furthermore, the coupling section 16 is affixed to the receiver 17 in astate where the movable leg section 18 is inserted into the receiver 17and a lower section of the coupling section 16 is fitted to the receiver17 and the stepped section 32 b of the plug body 32 is engaged with thestepped section 17 a. Thus, the movable leg section 18 is connected withthe coupling section 16 and with the guide tube 27 b via the receiver 17so as to be freely pivotable.

As illustrated in FIG. 13(a), the extension/retraction leg section 21 isinserted in a space between the engagement tube 19 and the inner tube 28so as to be freely slidable. Moreover, a male screw section 33 a isformed in the vicinity of the lower end 19 a of the engagement tube 19,and a female screw section 33 b which can be screwed with the male screwsection 33 a is formed at a part of an inner circumferential surface ofthe adjustment tool 22 b having an inner diameter formed in a steppedshape. In addition, an elastic member 34 made of synthetic resin isinstalled between the lower end 19 a of the engagement tube 19 and theadjustment tool 22 b so that a part of the elastic member 34 can beinserted into a space between the engagement tube 19 and theextension/retraction leg section 21.

Accordingly, when the adjustment tool 22 b is pivoted and moved in adirection indicated by the arrow F in FIG. 13(b), the elastic member 34is pressed by the adjustment tool 22 b and a part of the elastic member34 is pressed into a space between the engagement tube 19 and theextension/retraction leg section 21, and therefore theextension/retraction leg section 21 is pushed against the inner tube 28by the elastic member 34. As a result, frictional force between theextension/retraction leg section 21 and the inner tube 28 increases, andmovement of the extension/retraction leg section 21 in the direction ofthe cylinder axis with respect to the inner tube 28 is inhibited.Furthermore, as illustrated in FIG. 14, a pressing spring 10 isinstalled within the movable leg section 18 coaxially with the pressingspring 10 being fitted on the guide tube 27 b, an upper end 10 a of thepressing spring 10 abuts the plug body 32, and a lower end 10 b of thepressing spring 10 is affixed to the plug body 30.

When only the movable leg section 18 is pivoted in the direction of thearrow G₁ while the coupling section 16 and the engagement tube 19 areaffixed in the state illustrated in FIG. 15(a), the pulling spring 11pivots together with the movable leg section 18 as illustrated in FIG.15(b), and the engagement section 24 is pushed into a spiral space ofthe pulling spring 11. Thus, movement of the pulling spring 11 isinhibited, and the position of the engagement tube 19 in thelongitudinal direction with respect to the movable leg section 18 isaffixed. At this time, the pulling spring 11 in the extension/retractiondevice 1 b also functions as a length adjustment member.

That is, the extension/retraction device 1 b has an effect that thelength is decided by pivoting the movable leg section 18 with respect tothe engagement tube 19 and engaging the engagement section 24 with thepulling spring 11 which is a length adjustment member.

It is to be noted that, when only the movable leg section 18 is pivotedin the direction of the arrow G₂ while the coupling section 16 and theengagement tube 19 are affixed in the state illustrated in FIG. 15(b),the pulling spring 11 pivots together with the movable leg section 18 asillustrated in FIG. 15(a) and the engagement section 24 is removed froma spiral space of the pulling spring 11, and therefore the engagementstate of the engagement section 24 with respect to the pulling spring 11is released. As a result, restraint of the engagement tube 19 withrespect to the movable leg section 18 is released, and it becomespossible to extend and retract the extension/retraction device 1 b.

The extension/retraction device 1 b having such a structure has aneffect that the stopper assist tool 26 inhibits flexure of the pullingspring 11 in the process of pushing the engagement section 24 into aspiral space of the pulling spring 11. Thus, it is possible to reliablyengage the engagement section 24 with the pulling spring 11. Moreover,checking of the engagement state of the engagement section 24 with thepulling spring 11 is facilitated, since the pulling spring 11 isinstalled outside the movable leg section 18.

Accordingly, it is possible to achieve inspection, repair or the like ofthe engagement section 24 or the pulling spring 11 efficiently.Furthermore, it is also possible to decrease the diameter of the movableleg section 18 so as to downsize the entire device. Also, when thecoupling section 16 is coupled with another device or the like and theplug body 23 b of the extension/retraction leg section 21 is grounded,only the movable leg section 18 becomes pivotable independently of thecoupling section 16 and the engagement tube 19, and it is thereforepossible to achieve length adjustment of the extension/retraction device1 b safely and easily when the adjustment 22 b is operated to make theextension/retraction leg section 21 not pivotable with respect to theengagement tube 19. In addition, since the movable leg section 18 is notaffected even when the extension/retraction leg section 21 pivots, thereis no fear that the movable leg section 18 pivots and the engagementstate of the engagement section 24 with the pulling spring 11 isreleased unintentionally even when the installation state with respectto the ground is unstable and the extension/retraction leg section 21pivots, for example. Moreover, it is possible to catch a place of themovable leg section 18 other than the gripper 22 a, and this improvesthe handleability.

Example 3

An extension/retraction device of the present example will be explainedusing FIGS. 16 and 17 (corresponding especially to Claims 5 and 6). FIG.16(a) is a front view for illustrating the appearance of anextension/retraction device 1 c of the present example, and FIGS. 16(b)and 16(c) are front views for illustrating the appearance respectivelyof a movable leg section 35 and an engagement tube 36. Moreover, FIGS.17(a) and 17(b) are enlarged views of a cross section indicated by thearrow H-H in FIG. 16(a). It is to be noted that the same symbols areattached to constituent elements illustrated in FIGS. 1 to 15, andexplanation thereof will be omitted.

In the extension/retraction device 1 c, the pulling spring 11 in theextension/retraction device 1 b of Example 2 is not installed at themovable leg section 18 but an engagement section 24 is installed at amovable leg section 35, and the engagement section 24 in theextension/retraction device 1 b of Example 2 is not installed at theengagement tube 19 but a pulling spring 11 is installed at theengagement tube 36, as illustrated in FIGS. 16 and 17. That is, thestructure of the extension/retraction device 1 c and theextension/retraction device 1 b is substantially equal, except for themovable leg section 35 and the engagement tube 36.

The movable leg section 35 has a cylindrical shape, and an upper endthereof is connected with a coupling section 16 via a receiver 17 so asto be freely pivotable. Moreover, an opening 35 a is provided in thevicinity of a lower end of the movable leg section 35, and theengagement section 24 and a mounting plate 25 are installed on an innersurface of a cover 37 having an arc-like side view formed over theopening 35 a so as to project to the inside of the movable leg section35.

Furthermore, a recessed groove 36 a in which the pulling spring 11 is tobe held is provided along the longitudinal direction at an engagementtube 36 having substantially a cylindrical shape to be fitted in themovable leg section 35 so as to be freely slidable. In addition, withinthe recessed groove 36 a of the engagement tube 36, the pulling spring11 is installed parallel to the cylinder axis of the pulling spring 11so as not to come into contact with an inner surface of the movable legsection 35, and an extension/retraction leg section 21 is fitted in theengagement tube 36 so as to be freely slidable.

When only the movable leg section 35 is pivoted in the direction of thearrow I₁ while the coupling section 16 and the engagement tube 36 areaffixed in the state illustrated in FIG. 17(a), the engagement section24 pivots together with the movable leg section 35 as illustrated inFIG. 17(b). As a result, the engagement section 24 is pushed into aspiral space of the pulling spring 11. Thus, movement of the pullingspring 11 is inhibited, and the position of the engagement tube 36 inthe longitudinal direction with respect to the movable leg section 35 isaffixed.

That is, the extension/retraction device 1 c has an effect that thelength is decided by pivoting the movable leg section 35 and engagingthe engagement section 24 with the pulling spring 11. It is to be notedthat, when only the movable leg section 35 is pivoted in the directionof the arrow I₂ while the coupling section 16 and the engagement tube 36are affixed in the state illustrated in FIG. 17(b), the engagementsection 24 pivots together with the movable leg section 35 asillustrated in FIG. 17(a) and the engagement section 24 is removed froma spiral space of the pulling spring 11, and therefore restraint of theengagement tube 36 with respect to the movable leg section 35 isreleased and it becomes possible to extend and retract theextension/retraction device 1 c.

In an extension/retraction device 1 c having such a structure, simpleappearance and excellent design can be obtained since a projected partcaused by installation of the engagement section 24 or the pullingspring 11 is not generated on an outer surface of the movable legsection 35. Moreover, it is possible to achieve inspection, repair orthe like of the pulling spring 11 easily, since the pulling spring 11can be viewed easily by detaching the movable leg section 35 from theengagement tube 36.

It is to be noted that the structure of an extension/retraction deviceof the present invention is not limited to the cases illustrated asExamples 1 to 3. For example, a structure obtained by laminating aplurality of annular bodies may be installed instead of a pullingspring. In such a case, a plurality of places to be engaged with anengagement section exist in a length adjustment member laminatedannularly as in a spiral length adjustment member, and therefore it ispossible to achieve fine adjustment of the length of anextension/retraction device by engaging an engagement section at a spacebetween annular bodies. Moreover, a flat wire coil spring which hassubstantially a rectangular cross section and high strength can be usedas the pulling spring instead of a coil spring having a normal circularcross section.

An extension/retraction device according to any one of the abovedescribed embodiments of the claimed invention is not limited to a legsection of a tripod, a stepladder or the like, but can be applied to anelement which is a leg section of various devices and which has astructure that can be extended and retracted.

Further, while the invention has been described with respect to alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that other embodiments can bedevised which do not depart from the scope of the invention as disclosedherein. Accordingly, the scope of the invention should be limited onlyby the attached claims.

DESCRIPTION OF REFERENCE SYMBOLS

-   1 a . . . Extension/retraction device-   1 b . . . Extension/retraction device-   1 c . . . Extension/retraction device-   2 . . . Base-   2 a . . . Opening-   3 . . . Stationary leg section-   3 a . . . Opening-   4 . . . Movable leg section-   4 a . . . Guide hole-   5 . . . Engagement tube-   5 a . . . Upper end-   5 b . . . Lower end-   6 . . . Operating lever-   7 . . . Plug body-   8 . . . Projection-   9 . . . Gripper-   10 . . . Pressing spring-   10 a . . . Upper end-   10 b . . . Lower end-   11 . . . Pulling spring-   11 a . . . Upper end-   11 b . . . Lower end-   11 c . . . Wire-   12 . . . Core-   12 a . . . Upper end-   12 b . . . Lower end-   13 . . . Guide tube-   13 a . . . Upper end-   13 b . . . Lower end-   14 . . . Engagement section-   14 a . . . Stopper-   15 . . . Spacer-   15 a . . . Inner circumferential surface-   16 . . . Coupling section-   17 . . . Receiver-   17 a . . . Stepped section-   18 . . . Movable leg section-   18 a . . . Window section-   19 . . . Engagement tube-   9 a . . . Lower end-   20 . . . Cover-   21 . . . Extension/retraction leg section-   22 a . . . Gripper-   22 b . . . Adjustment tool-   23 a . . . Plug body-   23 b . . . Plug body-   24 . . . Engagement section-   24 a . . . Convex section-   24 b . . . Joint section-   24 c . . . Blade section-   24 e . . . Concave section-   25 . . . Mounting plate-   25 a . . . Side surface-   26 . . . Stopper assist tool-   26 a . . . Opening-   26 b . . . Columnar body-   27 a . . . Support body-   27 b . . . Guide tube-   28 . . . Inner tube-   29 . . . Spacer-   30 . . . Plug body-   31 . . . Guide member-   31 a . . . Spacer-   32 . . . Plug body-   32 a . . .Through hole-   32 b . . . Stepped section-   33 a . . . Male screw section-   33 b . . . Female screw section-   34 . . . Elastic member-   35 . . . Movable leg section-   35 a . . . Opening-   36 . . . Engagement tube-   36 a . . . Recessed groove-   37 . . . Cover

1. (canceled)
 2. An extension/retraction device comprising: acylindrical movable leg section; a spiral length adjustment member whichis parallel to a longitudinal direction of the movable leg section; anengagement section formed to be able to be engaged with the lengthadjustment member; an engagement tube on which the engagement section isaffixed so as not to be movable and which is to be fitted in the movableleg section so as to be slidable in a longitudinal direction; anextension/retraction member, which is installed in parallel with thelength adjustment member in the movable leg section, for biasing theengagement tube in a direction of separating from the movable legsection; a stationary leg section in which at least a part of theextension/retraction member and the engagement tube are held and whichis fitted in the movable leg section so as to be slidable in alongitudinal direction; and a guide member for guiding the stationaryleg section so as not to be pivotable and so as to be slidable withrespect to the movable leg section, wherein the engagement tube isinstalled so as to be pivotable about a cylinder axis of the movable legsection, wherein the length adjustment member has one end affixed to themovable leg section and the other end installed in the engagement tubeso as to be freely slidable in a longitudinal direction, wherein theengagement section is installed so as to penetrate a space of the lengthadjustment member while pivoting or so as to be removed from a spacewhile pivoting in conjunction with relative pivoting of the movable legsection and the engagement tube, and wherein an end of the engagementtube is supported by the stationary leg section so as to be pivotable.3. An extension/retraction device comprising: a cylindrical movable legsection; a spiral length adjustment member which is located parallel toa longitudinal direction of the movable leg section; an engagementsection formed to be able to be engaged with the length adjustmentmember; an engagement tube on which the engagement section is affixed soas not to be movable and which is to be fitted in the movable legsection so as to be slidable in a longitudinal direction; and anextension/retraction member, which is installed in parallel with thelength adjustment member in the movable leg section, for biasing theengagement tube in a direction of separating from the movable legsection, wherein the engagement tube is installed so as to be pivotableabout a cylinder axis of the movable leg section, wherein the lengthadjustment member has one end affixed to the movable leg section and theother end installed in the engagement tube so as to be freely slidablein a longitudinal direction, wherein the engagement section is installedso as to penetrate a space of the length adjustment member whilepivoting or so as to be removed from a space while pivoting inconjunction with relative pivoting of the movable leg section and theengagement tube, wherein the length adjustment member is not installedin the engagement tube so as to be slidable in a longitudinal directionwith an end thereof being affixed to the movable leg section butinstalled on an outer surface of the movable leg section outside theengagement tube with both ends thereof being affixed, and wherein awindow section is formed on at least a part of a side surface of themovable leg section along the cylinder axis so that the engagementsection is projected and can be engaged with the length adjustmentmember.
 4. The extension/retraction device according to claim 3,comprising: a coupling section installed at one of end sections of themovable leg section, in which the engagement tube is not fitted, so asto be freely pivotable about the cylinder axis; and a coupling memberfor coupling the coupling section with the engagement tube so as not tobe pivotable and so as to be slidable.
 5. The extension/retractiondevice according to claim 3, wherein the engagement tube is not providedwith the engagement section but provided with a recessed groove in whichthe length adjustment member is held and which is provided at a sidesurface along a longitudinal direction, wherein the length adjustmentmember is not installed at the movable leg section but provided in therecessed groove so as not to come into contact with an inner surface ofthe movable leg section, and wherein the movable leg section is notprovided with the window section but provided the engagement sectionwhich is installed on an inner surface so as to be able to be engagedwith the length adjustment member with relative pivoting with respect tothe engagement tube.
 6. The extension/retraction device according toclaim 4, wherein the engagement tube is not provided with the engagementsection but provided with a recessed groove in which the lengthadjustment member is held and which is provided at a side surface alonga longitudinal direction, wherein the length adjustment member is notinstalled at the movable leg section but provided in the recessed grooveso as not to come into contact with an inner surface of the movable legsection, and wherein the movable leg section is not provided with thewindow section but provided with the engagement section which isinstalled on an inner surface so as to be able to be engaged with thelength adjustment member with relative pivoting with respect to theengagement tube.
 7. (canceled)
 8. An extension/retraction devicecomprising: a cylindrical movable leg section; a length adjustmentmember laminated annularly at the movable leg section; an engagementsection formed to be able to be engaged with the length adjustmentmember; an engagement tube on which the engagement section is affixed soas not to be movable and which is to be fitted in the movable legsection so as to be slidable in a longitudinal direction; and anextension/retraction member which is installed in parallel with thelength adjustment member in the movable leg section, for biasing theengagement tube in a direction of separating from the movable legsection, a stationary leg section in which at least a part of theextension/retraction member and the engagement tube are held and whichis fitted in the movable leg section so as to be slidable in alongitudinal direction; and a guide member for guiding the stationaryleg section so as not to be pivotable and so as to be slidable withrespect to the movable leg section, wherein the engagement tube isinstalled so as to be pivotable about a cylinder axis of the movable legsection, wherein the length adjustment member has one end affixed to themovable leg section and the other end installed in the engagement tubeso as to be freely slidable in a longitudinal direction, wherein theengagement section is installed so as to penetrate a space of the lengthadjustment member while pivoting or so as to be removed from a spacewhile pivoting in conjunction with relative pivoting of the movable legsection and the engagement tube, and wherein an end of the engagementtube is supported by the stationary leg section so as to be pivotable.9. An extension/retraction device comprising: a cylindrical movable legsection; a length adjustment member laminated annularly at the movableleg section; an engagement section formed to be able to be engaged withthe length adjustment member; an engagement tube on which the engagementsection is affixed so as not to be movable and which is to be fitted inthe movable section so as to be slidable in a longitudinal direction;and an extension/retraction member, which is installed in parallel withthe length adjustment member in the movable leg section, for biasing theengagement tube in a direction of separating from the movable legsection, wherein the engagement tube is installed so as to be pivotableabout a cylinder axis of the movable leg section, wherein the lengthadjustment member has one end affixed e movable leg section and theother end installed in the engagement tube so as to be freely slidablein a longitudinal direction, and wherein the engagement section isinstalled so as to penetrate a space of the length adjustment memberwhile pivoting or so as to be removed from a space while pivoting inconjunction with relative pivoting of the movable leg section and theengagement tube, wherein the length adjustment member is not installedin the engagement tube so as to be slidable in longitudinal directionwith an end thereof being affixed to the movable leg section butinstalled on an outer surface of the movable leg section outside theengagement tube with both ends thereof being affixed, and wherein awindow section is formed on at least a part of a side surface of themovable leg section along the cylinder axis so that the engagementsection is projected and can be engaged with the length adjustmentmember.
 10. The extension/retraction device according to claim 9,comprising: a coupling section installed at one of end sections of themovable leg section, in which the engagement tube is not fitted, so asto be freely pivotable about the cylinder axis; and a coupling memberfor coupling the coupling section with the engagement tube so as not tobe pivotable and so as to be slidable.
 11. The extension/retractiondevice according to claim 9, wherein the engagement tube is not providedwith the engagement section but provided with a recessed groove in whichthe length adjustment member is held and which is provided at a sidesurface along a longitudinal direction, wherein the length adjustmentmember is not installed at the movable leg section but provided in therecessed groove so as not to come into contact with an inner surface ofthe movable leg section, and wherein the movable leg section is notprovided with the window section but provided with the engagementsection which is installed on an inner surface so as to be able to beengaged with the length adjustment member with relative pivoting withrespect to the engagement tube.
 12. The extension/retraction deviceaccording to claim 10, wherein the engagement tube is not provided withthe engagement section but provided with a recessed groove in which thelength adjustment member is held and which is provided at a side surfacealong a longitudinal direction, wherein the length adjustment member isnot installed at the movable leg section but provided in the recessedgroove so as not to come into contact with an inner surface of themovable leg section, and wherein the movable leg section is not providedwith the window section but provided the engagement section which isinstalled on an inner surface so as to be able to be engaged with thelength adjustment member with relative pivoting with respect to theengagement tube.